Method of applying acrylic functional carbonate ester coating to plastic substrates using high energy ionising radiation

ABSTRACT

Phosgene is reacted with a polyhydroxy containing compound to form a polychloroformate. The polychloroformate is then reacted with an acrylate containing one hydroxyl group in the presence of an acid acceptor to form the novel complex acrylate esters of this invention. The product is highly radiation-sensitive so that it may be polymerized by ionizing irradiation and forms a coating on plastic substrates which is hard, stain-resistant and abrasion-resistant.

United States Patent [191 Parker Jan. 15, 1974 METHOD OF APPLYINGACRYLIC FUNCTIONAL CARBONATE ESTER COATING TO PLASTIC SUBSTRATES USINGHIGH ENERGY IONISING RADIATION [75] Inventor: Gordon M. Parker, Apollo,Pa.

[73] Assignee: PPG Industries, Inc., Pittsburgh, Pa.

[22] Filed: Oct. 18, 1971 [21] Appl. No.: 190,327

Related US. Application Data [63] Continuation-impart of Ser. No.829,754, June 2,

1969, abandoned.

[52] US. Cl. 117/93.31, 117/l38.8 R, 1l7/138.8 E, 117/138.8 A, 117/138.8F, ll7/138.8 UA, 117/161UC,117/161UB, 204/159.22,

[51] Int. Cl. 844d l/50, C08f 11/00 [58] Field of Search l17/93.3l, 161UC, 117/161 UB, 161 R, 138.8 R, 138.8 B, 138.8

A, 138.8 F, 138.8 UA; 260/775 UA, 901; 204/159.22

[56] References Cited UNITED STATES PATENTS 2,370,572 2/1945 Muskat cta1. 260/77.5 UA

3,188,228 6/1965 Magat et al 1 17/9331 3,188,229 6/1965 Graham 3,361,842l/1968 Applegath et al. ll7/93.3l

FOREIGN PATENTS OR APPLICATIONS 606,716 8/1948 Great Britain 260/775 UAPrimary ExaminerWilliam D. Martin Assistant Examiner-John H NewsomeAttorney-Russell A. Eberly 5 7] ABSTRACT 8 Claims, N0 Drawings METHOD OFAPPLYING ACRYLIC FUNCTIONAL CARBONATE ESTER COATING TO PLASTICSUBSTRATES USING HIGH ENERGY IONISING RADIATION CROSS REFERENCE TORELATED APPLICATIONS This application is a continuation-in-part ofapplication Ser. No. 829,754 filed June 2, i969, now abandoned.

BACKGROUND OF THE INVENTION This invention, in general, deals with novelcompounds which are highly radiation-sensitive and which formunexpectedly good coatings on plastic substrates. The novel compoundsare complex arcylate esters containing at least two carbonate linkageswhich when subjected to low doses of ionizing irradiation polymerize toform extremely strong and stain-resistant materials.

The novel compounds used in this invention are complex arcylate esterswhich are derived from the reaction of a mono, di, or tri acrylatecontaining one hydroxyl group with a polychloroformate and preferably abischloroformate which is the reaction product of phosgene and apolyhydroxy containing compound. The product is a monomer having aplurality of carbonate linkages.

The polyhydroxy compound that is reacted with phosgene is generally apolyhydric saturated or unsaturated alcohol such as ethylene glycol,propylene glycol, butylene glycol, isobutylene glycol, trimethyleneglycol, pentamethylene glycol, or the corresponding polyglycols such asdi, tri, or tetraethylene glycol, or the corresponding propylene orbutylene or isobutylene polyglycols, glycerol, methyl glycerol,polyglycerols such as diglycerin or triglycerin, mannitol, sorbitol,polyvinyl alcohol, hydrated cellulose, cellulose monoacetate, cellulosemono b utyrate, starch, sugars, aromatic alcohols such as phthalylalcohols, may be reacted with phosgene in accordance with thisinvention. The preferred polyhydroxy compounds are glycols andpolyglycols.

Generally speaking, the preferred hydroxy compounds have the formulaR"(OH), wherein R" is a substituted or unsubstituted aryl, alkyl, orcycloalkyl group having from about 2 carbon atoms to about carbon atomsand x is a whole number from 2 to 4. The R" group may be substitutedwith any group that does not have an active hydrogen atom such as amine,thiol, etc., groups. Examples of substituted groups which may be usedare alkoxy, ketoxy, ester substituted groups and other substitutedgroups.

The reaction of phosgene with the polyhydroxy compound needs no solventor catalyst but a solvent may be used, if desired. It is carried out atfrom about -l0C. to about C. by bubbling phosgene gas through thepolyhydroxy compound at a rate which will not raise the temperature ofthe mixture above 50C. (This is an exothermic reaction.)

The reaction is generally equimolar but it is preferred to add a slightexcess of phosgene. The proportion of components, however, is notcritical. After the reaction is completed, the resultingpolychloroformate is heated from about 50C. to about 70C. to drive offdissolved hydrochloric acid and the product is then washed, dried andfiltered.

The product of the above reaction is a polychloroformate. The preferredpolychloroformates are bischloroformates such as ethylene glycolbischloroformate, di ethylene glycol bischloroformate, polyethyleneglycol bischloroformate, and the like. However, other polychloroformatessuch as the trischloroformate of trimethylolpropane or thetrischloroformate of glycerol may be used.

The mono, di, or tri acrylates that are reacted with thepolychloroformates obtained in the above manner contain one hydroxylgroup which contains the only active hydrogen atom in the compound. Inother words, the-compound may not contain other groups having reactivehydrogen atoms such as amines, thiols, etc. The most preferred of theseacrylates is the mono acrylate (hydroxy alkyl acrylate or methacrylate).Generally, these acrylates and methacrylates have the formula wherein Ris selected from the group consisting of hydrogen and methyl and R is asubstituted or unsubstituted alkyl group having from about two to about16 carbon atoms. Examples of these compounds are hydroxy ethyl acrylate,hydroxy ethyl methacrylate, hydroxy butyl acrylate, hydroxy laurylacrylate, hydroxy lauryl methacrylate, hydroxy isooctyl acrylate,hydroxy undectyl methacrylate, hydroxy 2,4,4-trimethylpentylacrylate,hydroxy 2,4,4-trimethylpentylmethacrylate, and the like. The alkylgroups may be substituted with halogens such as chlorine, alkoxyradicals, or R"COO- radicals wherein R is a saturated or unsaturatedhydrocarbon such as alkyl'or alkylene.

Other acrylates having one hydroxyl group which may be used here are thedi or tri acrylates such as l,3- glycerol diacrylate, 1,3-glyceroldimethacrylate, pentaerythritol triacrylate, trimethylol propanediacrylate, and the like.

The reaction of the acrylate with the bischloroformate takes place inthe presence of an acid acceptor. The acid acceptor is necessary to tieup the HC] that is split off from the reaction to prevent HCl additionto the double bond of the monomer. Any acid acceptor may be used but itis preferable to use an aqueous base or a tertiary amine. Examples oftypical acid acceptors that may be used are pyridine, trimethyl amine,aqueous sodium carbonate, triethyl amine, aqueous sodium hydroxide, andthe like.

A solvent is generally used for the acrylate so that the resulting saltis dispersed and the product is more easily filtered thus giving abetter yield. Any solvent that is insoluble in water and unreactive withphosgene may be used. The preferred solvents are benzene, toluene, ethylacetate, methylene chloride, trichloroethylene, and the like.

The reaction is carried out by adding the polychloroformate to a solventsolution of the acrylate and an acid acceptor such as pyradine.Generally it is preferred to react the polychloroformate and acrylate atlow temperatures of from about -l0C. to about 50C. As this reaction isalso exothermic, the rate of addition of the bischloroformate should below enough so that the temperature of the components do not exceed 50C.

The proportions of the components may be varied over a wide range butgenerally 1 mol of polychloroformate is reacted for every 2 mols ofacrylate. The relative amounts of the components are not critical. Alsoit is preferable to use at least 2 mols of acid acceptor for every molof polychloroformate so that all the HCl generated will be tied up.

The product of the reaction is filtered out, washed, and dried and thesolvent is stripped. The monomer obtained may be polymerized by peroxideaddition with heat or it may be polymerized by ionizing irradiation oractinic light.

The monomers prepared in this manner are extremely radiation-sensitiveand are polymerized by subjecting them to ionizing irradiation aftercoating on the plastic substrate.

The term irradiation, as used herein, means high energy radiation and/orthe secondary energies resulting from conversation of electrons or otherparticle energy to X-rays or gamma radiation. While various types ofirradiation are suitable for this purpose, such as X-ray and gamma rays,the radiation produced by accelerated high energy electrons has beenfound to be very conveniently and economically applicable and to givevery satisfactory results. However, regardless of the type of radiationand the type of equipment used for its generation or application, theuse thereof in the practice of the invention as described herein iscontemplated as falling within the scope of this invention so long asthe ionization radiation is equivalent to at least about 100,000electron volts.

While there is no upper limit to the electron energy that can be soapplied advantageously, the effects desired in the practice of thisinvention can be accomplished without having to go to above about20,000,000 electron volts. Generally, the higher the electron energyused, the greater is the depth of penetration into the massive structureof the materials to be treated. For other types of radiation, such asgamma and X-rays, energy systems equivalent to the above range ofelectron volts are desirable.

It is intended that the term irradiation include what has been referredto in the prior art as ionixing radiation which has been defined asradiation possessing an energy at least sufficient to produce ions or tobreak chemical bonds and thus includes also radiations such as ionizingparticle radiation" as well as radiations of the type termed ionizingelectromagnetic radiation".

The term ionizing particle radiation" has been used to designate theemission of electrons or highly accelerated nuclear particles such asprotons, neutrons, alphaparticles, deuterons, beta-particles, or theiranalogs, directed in such a way that the particle is projected into themass to be irradiated. Charged particles can be accelerated by the aidof voltage gradients by such devices as accelerators with resonancechambers, Van der Graaff generators, betatrons, synchrotons, cyclotrons,etc. Neutron radiation can be produced by bombarding a selected lightmetal such as beryllium with positive particles of high energy. Particleradiation can also be obtained by the use of an atomic pile, radioactiveisotopes or other natural or synthetic radioactive materials.

Ionizing electromagnetic irradiation is produced when a metallic target,such as tungsten, is bombarded with electrons of suitable energy. Thisenergy is conferred to the electrons by potential accelerators of over0.1 million electron volts (mev.). In addition to irradiation of thistype, commonly called X-ray, an ionizing electromagnetic irradiationsuitable for the practice of this invention can be obtained by means ofa nuclear reactor (pile) or by the use of natural or syntheticradioactive material, for example, cobalt 60.

Various types of high power electron linear accelerators arecommercially available, for example, the

ARCO type travelling wave accelerator, model Mark I,

operating at 3 to 10 million electron volts, such as supplied by HighVoltage Engineering Corporation, Burlington, Mass, or other types ofaccelerators as described in U.S. Pat. No. 2,763,609 and in BritishPatent No. 762,953 are satisfactory for the practice of this invention.

The monomers described herein will polymerize acceptably using any totaldosage between about 0.2 megarads and about 20 megarads. A rad isdefined as that amount of irradiation required to supply ergs per gramof material being treated and a megarad is 10 rads. The total dosage isthe total amount of irradiation received by the monomer.

The polymers formed have great utility as coatings for all types ofsubstrates such as protective coatings for wood, metal, and othersubstrates and they have the advantage of having superior stainresistance, scratch resistance, and a high degree of crosslinking.However, it has been found that when the monomers are coated ontoplastic substrates and subjected to high energy ionizing irradiation, achemical graft between the coating and substrate is formed, insuring astrong bond between coating and substrate.

The unexpectedly superior bonding of this particular coating is foundwith any plastic substrate. By plastic" it is meant that the material isa generally high molecular weight thermoplastic such as polyacrylates,such as polymethylmethacrylate, polybutylacrylate, and the like.Polycarbonates such as Lexan which is a product of phosgene andbisphenol A, polystyrene, acrylonitrile-butadiene-styrene copolymers.Polypropylene, polyethylene, polyvinyl chloride, polyformaldehyde, andthe like.

The coatings may be formed by coating the monomer onto the substrate byany conventional coating means such as roller coating, curtain coating,brushing, spraying, etc. The coated article is then cured by subjectingthe coating to ionizing irradiation. It is noted that many of themonomers have extremely low viscosity thus ensuring easy application, ifthe composition is to be used as a coating.

The use of ionizing irradiation to polymerize the monomers is especiallypreferable as this method makes it possible to polymerize the coating atextremely high speeds and thus eliminates the timeconsuming bakingsteps. As the use of ionizing irradiation requires no heating, thedanger of high temperatures damaging substrates which are extremelyheatsensitive such as plastic is eliminated. It is noted that the use ofheat adversely affects the dimensional stability and surface propertiesof many plastics.

it is also noted that the use of ionizing irradiation requires nosolvents, thus reducing the danger of poisonous and explosive solventvapors and that coatings formed by irradiating the monomers are morehighly crosslinked and are generally stronger coatings.

The following Examples set forth specific embodiments of the instantinvention. However, the invention is not to be construed as beinglimited to these embodiments as there are, of course, numerous possiblevariations and modifications. All parts and percentages in the Examplesas well as throughout the specification are by weight unless otherwiseindicated.

EXAMPLE 1 A flask equipped with a dry ice condenser was filled with 46grams of ethylene glycol and cooled to C. 196 grams of phosgene gas werebubbled through the ethylene glycol. The product formed was abischloroformate of ethylene glycol.

A flask equipped with a dry ice condenser was filled with 85.3 grams of2-hydroxyethyl acrylate, 250 milliliters of benzene, and 59 grams oftrimethyl amine. The flask was cooled to C. and 59.1 grams of thebischloroformate of ethylene glycol were added at a slow rate. Theproduct was washed with sodium hydroxide,

again washed with hydrochloric acid and finally washed with water andstripped. The final product which was a low viscosity, water-whiteliquid, had an OH value of 10.49, 1.41 percent chlorine and a yield of33 percent.

EXAMPLE 2 A flask equipped with a dry ice condenser was filled with 200grams of polyethylene glycol having a molecular weight of 200 and cooledto 0C. 196 grams of phosgene gas were bubbled through the polyethyleneglycol. The product was abischloroformate of polyethylene glycol.

A flask was filled with 63 grams of 2-hydroxyethyl acrylate, 54.5 gramsof pyridine and 200 milliliters of benzene. The flask was cooled to 5C.and 88.5 grams of the bischloroformate of the polyethylene glycol wereadded. The product was washed with dilute sodium hydroxide and thenwashed with dilute hydrochloric acid and finally washed with water andstripped. The final product, which was a low viscosity, water-whiteliquid, had an OH value of 0, 1.76 percent chlorine and an 84 percentyield.

EXAMPLE 3 A flask equipped with a dry ice condenser was filled with 82grams of diethylene glycol and cooled to 0C. Phosgene gas was bubbledthrough the diethylene glycol until the mixture contained 196 grams ofphosgene. The product formed was a bischloroformate of diethyleneglycol.

A flask was filled with 1 16.1 grams of 2-hydroxyethyl acrylate, 100grams of pyridine, and 100 milliliters of benzene. The flask was cooledto 5C. and 1 15.5 grams of the above bischloroformate of diethyleneglycol were added over a one-half hour period. The product was washedwith dilute sodium hydroxide and then washed with dilute hydrochloricacid and finally washed with water and stripped. The final product whichwas a low viscosity, water-white liquid, had an OH value of l 1.13 andcontained 1.9 percent chlorine.

EXAMPLE 4 A flask was filled with 130 grams of Z-hydroxyethylmethacrylate, 100 grams of pyridine, and 300 milliliters of benzene, andcooled to C. To this mixture, 115.5 grams of a bischloroformate ofdiethylene glycol were added dropwise. The reaction product wasfiltered, washed, and stripped.

The resulting product had a structure and had an acid number of 0.7, ahydroxy value of 2.28 and a Gardner-Holdt viscosity of E-F.

EXAMPLE 5 A diacrylate was formed by charging a vessel with 302.4 gramsof acrylic acid and 1.6 grams of hydroquinone and heating to 110C. Tothis mixture were then added 1.6 grams of N-methyl morpholine and 512grams of glycidyl acrylate. The reaction was continued until an acidnumber of 13.6 was attained.

A flask was filled with 1 12.5 grams of the diacrylate prepared aboveand 50 grams of pyridine and 400 milliliters of benzene. The flask wascooled to 10C. and 58 grams of the diethylene glycol bischloroformateprepared in Example 3 were added dropwise. The mixture was then heatedfor 1 hour at C. and washed. The resulting product had an acid value of0.84 and an OH value of 27.8.

EXAMPLE 6 A diacrylate was formed by charging a vessel with 316 grams ofmethacrylic acid and 1.62 grams of hydroquinone and heating to 110C. Tothis mixture were then added 1.62 grams of N-methyl morpholine and 497grams of glycidyl methacrylate. The reaction was continued until an OHvalue of 269 was obtained.

A flask was filled with 1 12 grams of the dimethacrylate prepared above,grams of pyridine and 400 milliliters of benzene. The flask was cooledto 10C. and 58 grams of the diethylene glycol bischloroformate preparedin Example 3 were added dropwise. The mixture was then heated for 1 hourat 40C. and washed. The resulting product had an acid value of 0 and anOH value of 34.9.

EXAMPLE 7 A flask was charged with 125 grams of a tri-acrylate of 60percent pentaerythritol tri-acrylate in pentaerythritol tetraacrylate,25 grams of pyridine, and 400 milliliters of benzene. The temperaturewas brought to 10C. and 27.4 grams of the bischloroformate of diethyleneglycol formed in Example 3 were added. The mixture was heated to 40C.for 1 hour and the product was filtered and washed. The yield was 77percent and the OH value was 33.6.

EXAMPLE 8 A trischloroformate was formed by the following method.

A reactor vessel was charged with 722 grams of glycerine and heated toC. in a nitrogen atmosphere. To the reactor were then added 14.4 gramsof an 85 percent solution of potassium hydroxide in water and stirred atC. The resulting mixture was charged to a pre-heated dry loop and purgedwith nitrogen. The mixture was heated to 200-230F. at 30-40 pounds persquare inch pressure and 2,088 grams of ethylene oxide were added. Thereaction was run for 6% hours. The resulting glycerine-ethylene oxideadduct, after purification by washing, had a neutral acid number and anOH number of 483.38.

A reaction vessel was charged with 429 grams of the above preparedglycerine-ethylene glycol adduct, 437 grams of phosgene and 200milliliters of chloroform. The reactants were cooled to -11C. andreacted for 2 /2 hours. The resulting trischloroformate had the formula:

o CH0 (CHzCH O); OCH1CHgO( JCH=CH I n HQO(CHZCHQO)I(IJOCH1CH1OC CH=CH1and had an acid valu e oTOTcohtained O percent chF) rine, and had ahydroxyl number of 15.70.

EXAMPLE 9 A trischloroformate was prepared as in Example 8.

A reaction vessel was charged with 65 grams of 2- hydroxyethylmethacrylate, 50 grams of pyridine, and 400 milliliters of benzene andcooled to l0-l5C. To the reactants were added dropwise for one-halfhour, 84.2 grams of the trischloroformate of Example 8, while thetemperature was maintained at l0-l5C. The resulting product afterpurification by washing had the formula 0 o can ll 8 6 CHzO(CHgCHzO)1OCH2CH2O =CH o 0 CH: g 8 HO(CHCHO) OCHgCHiO- =CH:

(I) (I) OH: HgO(CHzCHzOhJJOCHzCHzO-( J-CH:

and contained 1.05 perc ent chlorine, 556' 115311 Try droxyl value of18.38.

EXAMPLE 10 A 3-mil thick coating of the composition of Example 3 wascoated on a Lexan substrate by the drawdown technique. The coated panelwas then subjected to electron beam impingement in a nitrogen atmosphereat an accelerating potential of 400 KV and a tube current of 32milliamps having a beam scan of l X 20 inches. The total dose given thecoating was 5 megarads.

The resulting coating was a hard film which was tested for stain andsolvent resistance by staining the film with ink, mustard, andthimerosal. The coating was found to be completely resistant to thesematerials.

The mar resistance and adhesion of the coating to the plastic substratewas found to be excellent.

EXAMPLE 11 A 3-mil thick coating of the composition of Example 3 wascoated on an acrylonitrile-butadiene-styrene interpolymer substrate bythe draw-down technique. The coated panel was then subjected to electronbeam impingement in a nitrogen atmosphere at an accelerating potentialof 400 KV and a tube current of 32 milliamps having a beam scan of l X20 inches. The total dose given the coating was 5 megarads. Theresulting coating was a hard film which was tested for stain and solventresistance by staining the film with ink, mustard, and thimerosal. Thecoating was found to be completely resistant to these materials.

The coating was found to have excellent adhesion and mar resistance.

According to the provisions of the patent statutes, there is describedabove the invention and what are now considered to be its bestembodiments. However, within the scope of the appended claims, it is tobe understood that the invention can be practiced otherwise than asspecifically described.

1 claim:

1. A method of preparing a coated plastic substrate comprising applyingto the plastic substrate a composition comprising the reaction productof a polychloroformate which is the reaction product of phosgene and acompound having the formula R" (OH) wherein R" is a member of the groupconsisting of alkyl, aryl and cycloalkyl, and substituted alkyl, aryland cycloalkyl groups containing from about two carbon atoms to about 20carbon atoms wherein the substitution does not contain an activehydrogen atom and x is a whole number from 2 to 4 carried out at atemperature of from about l0C. to about 25C. and an acrylate having theformula wherein R is selected from the group consisting of hydrogen andmethyl and R is an unsubstituted or halogen, alkoxy or R"COO substitutedalkyl group wherein the alkyl radical has from about two to about 16carbon atoms wherein the reaction is carried out at a temperature offrom about l0C. to about 50C. in the presence of an acid acceptor andsubjecting the coated substrate to high energy ionizing irradiation.

u zffiieinethod aroma i whereiii'tliei't'al dosage of irradiation isfrom 0.2 to about 20 megarads.

:iffh'fidhbd or claim 1 wherein R" (on), is ethylene glycol.

4. The method of claim 1 wherein the acrylate is hydroxy ethyl acrylate.

5. The method of claim 1 wherein the plastic substrate is polymethylmethacrylate.

6. The method of claim 1 wherein the plastic substrate is the reactionproduct of phosgene and bisphenol A.

7. The method of claim 1 wherein the plastic substrate is polyethylene.

8. The coated substrate formed by the method of claim 1.

2. The method of claim 1 wherein the total dosage of irradiation is from0.2 to about 20 megarads.
 3. The method of claim 1 wherein R'''' (OH)xis ethylene glycol.
 4. The method of claim 1 wherein the acrylate ishydroxy ethyl acrylate.
 5. The method of claim 1 wherein the plasticsubstrate is polymethyl methacrylate.
 6. The method of claim 1 whereinthe plastic substrate is the reaction product of phosgene and bisphenolA.
 7. The method of claim 1 wherein the plastic substrate ispolyethylene.
 8. The coated substrate formed by the method of claim 1.